1. Field of the Invention
The present invention relates to an engine of a compression-ratio variable type, comprising a connecting rod connected at one end to a piston through a piston pin, a subsidiary rod connected to a crankshaft through a crankpin and to the other end of the connecting rod, a control rod connected at one end to the subsidiary rod at a location displaced from a connected position of the connecting rod, a support shaft turnably carried in an engine body, and an eccentric shaft mounted at an eccentric location on the support shaft and connected to the other end of the control rod, the turned position of the support shaft being changed to change the compression ratio.
2. Description of the Related Art
There is a conventional engine of a compression-ratio variable type known from, for example, Japanese Patent Application Laid-open No. 9-228858, in which a subsidiary rod connected to a crankshaft and a piston are connected to each other through a connecting rod, and an eccentric shaft mounted at an eccentric location on a support shaft turnably carried in an engine body and the subsidiary rod are connected to each other through a control rod, the compression ratio of the engine being changed by changing the turned position of the support shaft.
In the conventional engine, the turned position of the support shaft is changed by driving the support shaft in turning by an actuator such as an electric motor and a cylinder, to thereby change the compression ratio. However, an expansion load and a compression load are applied to the control rod by the combustion in the engine and inertia. For this reason, a shock load is applied to the actuator such as the electric motor and the cylinder and hence, a means for moderating such a shock must be mounted between the actuator and the support shaft, resulting in a complicated arrangement.
If the direction of turning of the support shaft is limited to one direction, the support shaft can be turned utilizing the expansion load and the compression load applied to the control rod by the combustion in the engine and the inertia. With this arrangement, the actuator for driving the support shaft in turning is not required. However, a limiting means for limiting the turned position of the support shaft at a plurality of points is required, and when the turned position of the support shaft is limited, a shock is applied to contact portions of such a limiting means and the support shaft, so that it is necessary to moderate such a shock.
Accordingly, it is an object of the present invention to provide an engine of a compression-ratio variable type, wherein the support shaft is turned utilizing the combustion in the engine and the inertia, and moreover, the shock generated upon limiting of the turned position of the support shaft can be moderated in a simple arrangement.
To achieve the above object, according to a first feature of the present invention, there is provided an engine of a compression-ratio variable type, comprising a connecting rod connected at one end to a piston through a piston pin, a subsidiary rod connected to a crankshaft through a crankpin and to the other end of the connecting rod, a control rod connected at one end to the subsidiary rod at a location displaced from a connected position of the connecting rod, a support shaft turnably carried in an engine body, and an eccentric shaft mounted at an eccentric location on the support shaft and connected to the other end of the control rod, the turned position of the support shaft being changed to change the compression ratio, wherein the engine further includes a one-way clutch mounted between the support shaft and the engine body in such a manner that the direction of turning of the support shaft is limited, a turned-position limiting means for limiting the turned position of the support shaft selectively at a plurality of points, and buffering means for moderating a load applied to at least one of the support shaft and the turned-position limiting means upon changing-over of the compression ratio.
With such arrangement of the first feature, an expansion load and a compression load are applied to the control rod by the combustion in the engine and inertia, whereby the support shaft and the eccentric shaft are turned in the direction limited by the one-way clutch, when the compression ratio is changed over. Therefore, an actuator for directly turning the support shaft is not required. Moreover, the load applied to at least one of the support shaft and the turned-position limiting means when the compression ratio is changed over, can be moderated by the buffering means.
According to a second feature of the present invention, in addition to the first feature, a flywheel is secured to the crankshaft so that a rotational force is transmitted from a recoil starter to the flywheel in response to the starting operation of the engine; the buffering means comprises an output member disposed coaxially with the crankshaft in such a manner that the rotational force in the same direction as that of the recoil starter can be transmitted to the flywheel, and the rotation thereof is limited when the recoil starter is not operated, an input member coaxial with the output member, and a spiral spring mounted between the output member and the input member; and a torque transmitting means is mounted between the support shaft and the input member so that it transmits the rotational force in a direction to wind up the spiral spring from the support shaft to the input member until the completion of the winding-up of the spiral spring, but it permits the support shaft to be raced after the completion of the winding-up of the spiral spring.
With such arrangement of the second feature, when the compression ratio is changed over, the rotational torque of the support shaft is transmitted to the input member of the buffering means through the torque transmitting means, whereby forces are accumulated in the spiral spring by the winding-up of the spiral spring, and the moderation of a shock can be achieved by absorbing a load applied to the support shaft by the spiral spring. Namely, while the support shaft is turned to a next turning-inhibited position by the turned-position limiting means when the compression ratio is changed over, the rotational torques applied to the support shaft can be buffered and accumulated by the spiral spring of the buffering means. During accumulation of the force in the spiral spring, the rotation of the output member is limited, and when the recoil starter is started at the next start of the engine, the spring force accumulated in the spiral spring is transmitted from the output member to the flywheel. Thus, even if the expansion load on the recoil starter is alleviated, the engine can be started sufficiently.
According to a third feature of the present invention, in addition to the arrangement of the first feature, limiting abutments are provided on the support shaft at a plurality of points axially spaced apart from each other with their positions displaced in a circumferential direction of the support shaft; an actuator is connected to a limiting member for driving the limiting member in turning, the limiting member being carried in the engine body to constitute a portion of the turned-position limiting means so that it can be turned about an axis perpendicular to the support shaft to come into abutment alternatively against one of the limiting abutments to limit the turned position of the support shaft; and the buffering means is interposed between the limiting member and the engine body in order to moderate an axial shock upon the abutment of the alternatively selected limiting abutment against the limiting member.
With such arrangement of the third feature, the turned position of the support shaft can be limited in such a manner that the limiting member is brought into abutment against one of the plurality of limiting abutments provided on the support shaft by turning the limiting member by the actuator, whereby the compression ratio can be changed. In this case, a shock in a direction perpendicular to the support shaft is applied to the limiting member by the contact between the limiting member and one of the limiting abutments, but the shock can be moderated by a simple arrangement in which the buffering means is interposed between the limiting member and the engine body. Thus, it is possible to avoid the application of the shock to the actuator for driving the limiting member and to enhance the durability reliability, while avoiding an increase in sizes of various members such as the support shaft and the limiting member due to increases in their strengths. Moreover, it is also possible to suppress to a low level a sound generated when the limiting member is brought into contact with one of the limiting abutments.
According to a fourth feature of the present invention, in addition to the first feature, the buffering means is mounted between the support shaft and the engine body to moderate the radial load applied from the control rod to the support shaft.
With such arrangement of the fourth feature, when the compression ratio is changed over, a large load is applied to the support shaft and the turned-position limiting means, but the radial load applied to the support shaft is moderated by the buffering means. Therefore, it is possible to enhance the durability reliability, while avoiding increases in sizes of various members such as the support shaft and the turned-position limiting means due to increases in their strengths. Moreover, it is also possible to suppress to a low level a sound generated when the turned position is limited by the turned-position limiting means.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.